This invention relates generally to cables, and more particularly, to high-frequency cables with noise suppression features.
Cables are used to interconnect pieces of electronic equipment. For example, cables that are compliant with the Digital Video Interface (DVI) standard are used to interconnect personal computers and computer monitors. Universal serial bus (USB) cables are commonly used to interconnect personal computers with peripherals such as music players, digital cameras, and printers.
Cables that carry high frequency signals may emit undesirable radio-frequency electromagnetic radiation and may be subject to radio-frequency noise from external sources. This is particularly the case in cables that do not use expensive high-quality coaxial termination arrangements. To minimize the impact of external radio-frequency noise sources and to reduce radio-frequency emissions, high-frequency cables are commonly shielded using conductive shielding such as braided copper, spiral windings of copper tape, spiral windings of thin copper wire, and metallized polymer. The conductive shielding serves to prevent external signals from coupling onto the signal wires in the cable and minimizes radio-frequency emissions from the cable that could adversely affect nearby electrical equipment.
Particularly when very high frequencies are involved (e.g., signals in the upper megahertz and lower gigahertz range), the use of conductive cable shielding is unable to eliminate all adverse radio-frequency effects. In typical arrangements, the conductive shield of a cable is shorted to the ground of the electrical equipment to which it is connected. If the electrical equipment that is attached to cable exhibits ground noise, the ground noise can be coupled onto the conductive shielding of the cable. Unless corrective measures are taken, the coupled ground noise can cause the conductive shielding to emit undesirable radio-frequency electromagnetic radiation.
Ferrite loaded magnetic cable noise suppressors have been developed to address these problems. Magnetic cable noise suppressors are commonly based on toroidal ferrite beads or tubular ferrite profiles. With this type of arrangement, a cable noise suppressor is placed at the end of a cable where it surrounds the signal wires in the cable. The noise suppressor attenuates radio-frequency noise by creating a large impedance at high electromagnetic frequencies.
Ferrite beads tend to be unsightly, so less intrusive noise suppression arrangements have been developed that are based on sheets of high-permeability magnetic material. Such arrangements have not been widely used in practice due to issues with manufacturability, cost, and complexity.
It would therefore be desirable to provide improved cables with noise suppression capabilities.